An acquisition usually hands you a second procedure library with its own templates, numbering and approval process, and the easy choice is to leave it alone until someone has time to merge the two. The risk is that both libraries keep drifting and nobody is sure which standard applies at which site.
The practical approach is to decide what is an enterprise standard and what is genuinely site specific, then bring both libraries into one structured system so they follow the same review process going forward. Having every procedure in the same step based format is what makes the comparison possible in the first place, and it is what lets a change to the standard reach every site that uses it instead of only the ones someone remembered to update.