Quick Question...

[drone]

Whoa, some necromancy afoot! It's like it's Halloween or something!

Welcome to the Org, bunt0025!

For the upgrades, the clues are in the build prod file, column 17. I believe the UPGRADE_*(N) is like a cap, the highest one will take effect. So with vanilla MTW/VI, the values are:
Church: UPGRADE_MORALE(1)
Monastery: UPGRADE_MORALE(1)
Reliquary: UPGRADE_MORALE(2)
Cathedral: UPGRADE_MORALE(3)

However, the added benefits come from the population happiness bonuses, which do stack:
Church: +20%
Monastery: +10%
Reliquary: +30%
Cathedral: +40%

Edit-> I forgot, the religious conversion bonuses stack as well, so there is even more benefit to having these building:
Church: 10% conversion rate
Monastery: 10%
Reliquary: n/a
Cathedral: 15%

[DEB8]

For the upgrades, the clues are in the build prod file, column 17. I believe the UPGRADE_*(N) is like a cap, the highest one will take effect. So with vanilla MTW/VI, the values are:
Church: UPGRADE_MORALE(1)
Monastery: UPGRADE_MORALE(1)
Reliquary: UPGRADE_MORALE(2)
Cathedral: UPGRADE_MORALE(3)

Makes sense considering the bonuses noted elsewhere at F1.

However, the added benefits come from the population happiness bonuses, which do stack:
Church: +20%
Monastery: +10%
Reliquary: +30%
Cathedral: +40%

Edit-> I forgot, the religious conversion bonuses stack as well, so there is even more benefit to having these building:
Church: 10% conversion rate
Monastery: 10%
Reliquary: n/a
Cathedral: 15%

Interesting - Thanks.