PP is both actual and calculated. A calculated PP occurs during a BT effort where you sprint during a maximal effort while under fatigue. The theoretical number could be higher than the actual number you have achieved in the past.
OTOH if you suspect power spikes in your historical data an easy way to handle that is to view the activity table, enable Max Power using Edit Columns, sort by that column, mark any problem entries, then select Flag in upper right. That prevents those entries from affecting signature calculations.
PP is the least sensitive number when it comes to the signature algorithm. For example, it is not uncommon to have a lower PP during indoor season and bump it back up as soon as you head outdoors. You don’t want a large difference while training, but within ballpark is sufficient since Xert is recalculating your signature after every activity or lack of.
You can use Advanced MPA to make signature adjustments. See this article for details –
What is Advanced MPA? – Xert (baronbiosys.com)
Also, podcast #17 discusses signature adjustments and handling errant data –
The Xert Breakthrough Lab Podcast – Xert (baronbiosys.com)