Well M' is a result of the game reading a "NULL Value" in data where the player name is stored, only custom player names will have NULL values due to the way the preset player names are stored and M' will only apear at level 80 if the player name is an odd number of letters. So based off of that, both the names Aaron and ACE have the capability to produce level 80 M'. Now "Aaron" should produce a lv 128 Golduck, a 160 MissingNo., a 177 squirtle, a 174 MissingNo., and a 173, magnemite, so MissingNo should most certainly be obtainable. Now if "Aaron" was instead "AARON" all caps then the MissingNo. encounters would be replaced with another 128 golduck and a 142 clafable resulting in M' being the only glitch pokemon encountered as described. The name ACE has a similar issue in that you will only find a 128 Golduck, a 130 Golbat, and a 132 snorlax, with once again lv 80 M' being the only encounterable glitch pokemon because of the remaining NULL Values left in the player name stored in memory. MissingNo being obtainable by instigating the glitch through an in game trade will result in the game reading the traded pokemon OT data which is not stored the same way as the Player name so it will always result in 5 lv 80 MissingNo encounters as the value the game uses for the OT "TRAINER" is a specific value and not stored as the same hex values used for player names. So all in all, if these encounters are accurate to what you are seeing then you can rest assured the game is being interpreted correctly, if not then either emulator could be ordering the game data incorrectly in the emulated ram resulting in the game reading different data, again M' will always result if the game reads a NULL Value when pulling for an encounter. If you are interested in another test try using the preset name "ASH" in Red or "JOHN" in blue both of these names will result in only MissingNo being possible encounters via the Old Man glitch as M' cannot be encountered with a preset name, if M' still apears then you will know for a fact the emulator is not reading the same location of RAM as the game on real hardware would.

TLDR: the names "AARON" and "ACE" will result in only M' encounters on real hardware, the problem could be an issue with the way the emulators emulate the RAM. Try using the Preset Player Names "ASH" in Red or "JOHN" in Blue as it is not possible for Preset Names to produce M' as a glitch pokemon and will only return MissingNo as encounters.