You may have seen John Sargent's contributed notes for the FAQ on dealing with speaker grill mounting that you may find interesting, plus there's other notes above and below that.
https://brickboard.com/FAQ/700-900/RadioAntenna.htm#DoorSpeakerCovers

There's an additional radio topic area of the FAQ as a descriptive feature article on stereo installation
https://brickboard.com/FAQ/700-900/RadioStereoInstall.htm

If you search around with google there are a number of Volvo forums where people discuss speaker fitment issues, including that one you found on t-bricks. Click on the following refined general search to see them
https://www.google.com/search?q=volvo+door+speakers+740+OR+940+OR+700+OR+900

As for Crutchfield listing inaccuracies for suitable speakers, my understanding is that some of those may be speakers that people successfully managed to install using adapters or modifications to the mounting area. I recall that if you read the fine print that none are listed as direct fitment. Last I determined there are no commonly avilable speakers that are plug and play for door mounting other than used. 240 front door speakers are even worse to replace with even less clearance to the glass.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now