(I just noticed this is a duplicate post to Technologies moved from House of Wisdom can be researched in multiple buildings at the same time if this thread I have opened can be closed / removed please do. Thanks)
It appears Abbasid can research Phalanx from multiple barracks at once (if all researched at the same time)
I was playing a 2v2 Quick-match today when my Abbasid teammate made eight barracks and researched Phalanx multiple times at the same time leading to spearmen with a >75 tile attack range allowing them to attack units multiple screens away, from testing it appears that there isn’t a limit to the number of times this can be researched at once so I suspect there isn’t an upper limit.
I played this match on the most recent patch earlier today (Update 8324 - 5.0.8324.0)
(unfortunately as a new member here I had to add these as separate replies as I’m missing the discourse permissions for it)