A list of changes to the Munro list and database of Munros and tops can be found at The Database of British and Irish hills.
The list is maintained by the Scottish Mountaineering club (SMC) and is published in the SMC Journal. As far as I am aware, an update is only published when there is a change to the list. This is normally because of new survey data putting a mountain above or below 3000’ (914.4m) or changes in whether the mountain is a full Munro or a top (subsidiary peak).
The changes are summarised below:
1891: Munro’s first list published – 538 summits over 3000’, 282 of which are separate mountains. In modern terminology, that is 282 Munros with the rest being Munro tops.
1921: First revision after Munro's death. Mostly changes in what is a top or full Munro – 276 Munros.
1933: A few more switches between Munros and their associated tops – still 276 Munros.
1953: A couple more switches in location of the Munro peak. Beinn Tarsuinn added as Munro – 277 Munros
1969: Some coordinates updated; no changes to Munros/tops.
1974: Some changes between Munros and tops. Beinn a' Chlaidheimh (see 2012) and Ruadh Stac Mòr as Munros. First edition to give 6 figure grid references of the peaks. - 279 Munros.
1981: Various changes, several Munros demoted to tops – 276 Munros.
1984: Beinn Teallach promoted to Munro, several GR updated -277 Munros.
1990: Minor changes to some GRs – 277 Munros.
1997: Several tops promoted to full Munros - 284 Munros.
2009: Sgùrr nan Ceannaichean demoted – 283 Munros.
2012: Beinn a' Chlaidheimh demoted – 282 Munros.