It happens more often than you would think: you read an announcement listing a full run of dates, then a newer video description shows fewer cities. Before anything else, slow down. A description is a short piece of text written for a specific purpose on a specific day. Teams trim lists to fit a character limit, reorganize them by region, or write the text for just one leg of the tour. A shorter list tells you that the post covers less. It does not tell you that anything was taken off the calendar.
The most important habit is simple: never treat a missing line as a cancellation. The reliable sign of a change is an explicit notice, and it uses plain words such as postponed, cancelled, rescheduled or added, coming from the act or the promoter. If City A appears in the older post and is absent from the newer one, but no notice says anything about City A, then what you have is a gap in one post, not an announcement. We hold that gap as an open question and do not write it up as news.
Next, go to the places that are usually kept current. Most posts link to the tour's official site or to the ticketing pages, and those are updated when something truly changes. Then compare the two lists line by line: date, weekday, city and venue. Many apparent changes turn out to be typos, a swapped weekday, or a venue name reformatted with a different spelling or an abbreviation. Also check whether the newer list simply adds a block, such as a finale or a new leg. That is additive information that sits beside the earlier list; it does not replace it.
Sometimes two posts really do disagree and nothing explains it. In that case, resist the urge to pick the version you like better. Keep both versions in your notes, with the date you read each one, and wait for an official clarification. Be honest about the limits too: posts do not always explain their edits, and a post can be updated after you read it. So record when you looked, check back at the official pages before you book travel or hotels, and treat a confirmed notice as the only thing that settles it.