The very PDF you link to has part of the answer. See page 15 (in the PDF, not page number 15 as the book numbers it), for a list of other titles from the author, which includes this:
*Dodu and Other Stories (1943)
*Cyclone and Other Stories (1945)
An Astrologer’s Day and Other Stories (1947)
*Lawley Road and Other Stories (1956)
A Horse and Two Goats (1970)
Malgudi Days (1982)
Under the Banyan Tree and Other Stories (1985)
The Grandmother’s Tale and Selected Stories (1993)
*Published in India only
And looking around in Google Books, I found this snippet from R. K. Narayan as a novelist by P. S. Sundaram (1988), which says:
The distribution of stories is as follows:
A) Malgudi Days (1943) 19 stories
So it seems certain that some of the stories included in the 1982 book were not in the original publication and were published after it. Lawley Road and other stories is stated in the Penguin publications as having been published in 1956, so Narayan definitely wasn't predicting a future date of Indian Independence back in 1943.
Looking further, I found an article titled Analysis of R. K. Narayan’s Stories by Nasrullah Mambrol, stating:
Among the nineteen stories in Narayan’s first collection, Malgudi
Days, there are two stories, “Old Bones” and “Neighbours’ Help,” that
are laced with supernatural elements. This volume includes such
memorable stories as “The Gold Belt,” “The White Flower,” “An End of
Trouble,” and “Under the Banyan Tree.” [...]
One of the finest stories in the collection, “The Mute Companions,”
centers on the ubiquitous Indian monkey[.] [...].
Malgudi Days, it should be noted, is also the title of a later collection, published in the United States in 1982. Eight of the
thirty-two stories in this collection—“Naga,” “Selvi,” “Second
Opinion,” “Cat Within,” “The Edge,” “God and the Cobbler,” “Hungry
Child,” and “Emden”— were previously uncollected; the remaining
stories were selected from Narayan’s two earlier volumes, An
Astrologer’s Day and Lawley Road.
In Short Stories of R.K. Narayan, H. C. Trivedi and N. C. Soni (Indian Literature Vol. 16, No. 3/4 (JULY—DECEMBER 1973), pp. 165-179) state:
Malgudi Days is another collection of nineteen fresh and original stories out of which two stories — Old Bones and Neighbour's Hip deal with the supernatural element. The collection contains delightful stories like The Gold Belt, The White Flower, An End of Trouble, and Under the Banyan Tree. [...] Gardens introduces sparrows and The Mute Companions, a monkey. [...]
Cyclone and other Stories
This collection brings us a fresh stock of eighteen stories that
mirror quite accurately Indian life and character. The remarkable
quality of these stories is the ingenuity of their plots. The
Doctor's Word, An Astrologer's Day, The Roman Image are good
illustrations of this fact. [...]
An Astrologer's Day and other stories
Those who have read the earlier collections may not find this volume very interesting as twenty-four stories out of the collection of thirty have been reproduced here. Of the six remaining stories The Tiger's Claw, Watchman, and Crime and Punishment deserve careful consideration. [...]
Lawley Road and other Stories
The volume contains twenty-eight stories out of which fourteen have
been reprinted from the earlier collection. However, stories like
Lawley Road, The Marty's Corner, Wife's Holiday and Half-a-Rupee are really good. Uncle's Letters and Another Community mark a departure from the traditional stories. [...]
The original version of An Astrologer's Day, available on archive.org has 30 stories. We can see that Old Bones and Under the Banyan Tree are listed there.
History of Indian Literature: 1911-1956, struggle for freedom: triumph and tragedy
by Sisir Kumar Das (Sahitya Akademi, 2005) mentions one more title from the 1943 Malgudi Days:
The Malgudi Days is one of the best collections of stories he wrote.
Its themes include [...] an artist refusing to accept an award
convinced that he failed in his mission ('The Comedian') [...].
Another useful resource is Audrey E. Barlow's PhD thesis, A critical study of the autobiographical elements in the fictional works of R. K. Narayan (2005), specifically Chapter V: Subjectivity in his short stories. In footnotes, Barlow has noted some stories which have appeared in both 1943 and 1982 versions of Malgudi Days:
- "Father's Help"
- "A Shadow" (also in Lawley's Road (1956))
- "A Willing Slave"
And for some other tales in 1982 Malgudi Days:
- "Lawley Road", "Trail of the Green Blazer" and "The Martyr's Corner" are originally from Lawley Road and other stories (1956)
- "Leela's Friend" and "Engine Trouble" are originally from Dodu and Other Stories (1943).
To summarize a bit:
- Malgudi Days (1943) had 19 stories, of which I could find mentions of these titles:
- "Old Bones"
- "Neighbours’ Help"
- "The Gold Belt"
- "The White Flower"
- "An End of Trouble"
- "Under the Banyan Tree"
- "The Mute Companions"
- "Father's Help"
- "A Shadow"
- "A Willing Slave"
- "The Comedian"
- Dodu and other stories first show:
- "Leela's Friend"
- "Engine Trouble"
- Cyclone and other stories (1945) has the first appearance of:
- "An Astrologer's Day"
- "The Missing Mail"
- "The Doctor's Word"
- "The Blind Dog"
- "Fellow Feeling"
- "Such Perfection".
- An Astrologer's Day and other stories (1947) first includes:
- "The Tiger's Claw"
Lawley Road (1956) marks the first appearance of:
- "Lawley Road"
- "Trail of the Green Blazer"
- "The Martyr's Corner"
- "Wife's Holiday"
Malgudi Days (1982) has 32 stories of which 8 are new, and at least 14 originally appeared in a collection other than the 1943 Malgudi Days (2 from Dodu, 7 from Cyclone, 1 from An Astrologer's Day and 4 from Lawley Road).
That leaves 10 possible stories common to both 1943 and 1982. And at least 9 titles from 1943 were not included in 1982, also leaving 10 possible common stories. We know three of these ("Father's Help", "A Shadow", "A Willing Slave"), but I can't be sure about the remaining 7:
- "Gateman's Gift" (this could plausibly be from 1943 - given retirement after 25 years of service starting around 1918).
- "The Snake-Song"
- "Forty-Five A Month"
- "Out Of Business"
- "The Axe"
- "Mother And Son"
Of course, many of these stories were originally originally published in The Hindu newspaper, before being included in these collections.
So, if there's no way to derive 19 from 16, 8 and 8, well, after the first three collections (Dodu and Other Stories, Malgudi Days (1943) and Cyclone and other stories), the various collections each included stories that were included in previous collections as well as new ones.