... the pictures are now in reverse chronological order with the newest first. Do you know of a way to get them back in order without renumbering all the individual pictures?
If you are using the newer "Drag and drop" editor, there is a tab under gallery edit for sequencing that has a pull-down with several options including 'Reverse current order'. In the old legacy editor I don't recall if there is a reverse order choice. (It took me a while, but I have pretty much permanently transitioned to the newer version.) Other options in the new editor include sorting by timestamp or by filename, so perhaps one of those would address your problem.
I apply here a standard caveat -- I have never used the resequence features in the new editor, so have no experience as to whether it works or has some of the usual PBase idiosyncrasies. I usually go into 'Content' in the Drop&Drag editor and just drag the thumbnails to the order I want. I normally get most of what I want from the upload, but that process does have a quirk that doesn't always quite obey the set sequence in loading a list of files. As in the last in the sequence may wind up second in the group (I suspect something weird in the coding to test when the process is done).
Maybe this will help ...
DaveT