Merging into wrong album

Because various artist albums do not appear as one album I have had to do a lot of merging. The problem I have (can this only be me?) is that I forget to unselect the album before and so the new tracks are merged into another album.
Trying to unmerge them seems hard to do, short of doing all sorts of editing of the source files and refreshing.
Any ideas? Or have I missed something obvious?
Thanks

Various Artists albums can appear as one album if you want them to:

Many thanks - I’ll do this. The odd thing is that it clearly knows they are from the same album. I had not left the album artist blank.
I use MP3Tag and like it.
As an after thought, it would have avoided a lot of stress if, when selecting a lot of tracks to merge, that it gave a list of the tracks and the merged into folder - just as a final check.
Thanks again Andy