In the case of Armenian Heavy Cavalry, what limits the availability is it is set to MUSLIM in Column 54. If you want the unit available to other cultures you must
either add the other cultures here, e.g. "CATHOLIC, ORTHODOX, MUSLIM, PAGAN" (you must include the quote marks with a list here) OR you can just delete the word MUSLIM and resave the file*. You can select any combination of cultures here to your taste.
Column 17 is relevant because the building requirements may limit it to a particular culture - you can make Nizari for instance available to all cultures, but they need a GRAND_MOSQUE, so in practice they'll still be limited to Muslim factions.
Column 50 allows you to list specific factions, so for instance if you leave column 54 blank (all cultures) you can change the current entry in column 50 ( ALL_FACTIONS ) to make a list of the factions you want, eg "FN_ENGLISH,FN_TURKISH" Obviously this would make your AHCs available to those two factions only. Now, because these columns are filters, if you keep column 54 showing as MUSLIM, then only the Turkish would have them, because the English are not a Muslim faction.
Other notes: the spaces in {HORSE_BREEDER2} and { HORSE_BREEDER2 } make no difference beyond making reading easier
But {HORSE_BREEDER 2} would break it because the label is no longer the same as in the BUILD_PROD file.
Once you have Gnome, you'll also see that Turcopoles are limited to CATHOLIC factions in column 54. The Muslim factions have their own horse archer units, the turcopoles are there to represent units who fought alongside the Crusaders against their co-religionists.
Finally, regarding the tech chart -it's
mostly correct, but has enough errors in it to make it useless in this regard.