SureFire have developed their products over the course of many years.
There has been some slight changes to the lengths of the body and various components but they remain interchangeable.
with respect Paladin is more likely to have experienced an issue with the Z32 and the spring contacts of the Lamp Assembly (and perhaps the spring contact of the TailCap) rather than an issue of the 6P body and A19 body extender combination.
If the TailCap spring and/or the Lamp Assembly +ve spring contact have been compressed then there is a chance of the proper contact not being established. Alternatively, if the TailCap spring is long then it could push the batteries too far forwards and since the 6P is not a WeaponLight body this would move the lamp assembly forwards compressing the Z32's shock isolation foam and if then the Lamp Assembly's -ve spring contact is too short it could not form reliable contact.
Anyway, them be my thoughts...
The 6P+A19 etc does create a three-SF123A body. I have used A19's on many different SureFires in various combinations without issue.
For example:
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