Tom, it appears that you have created two free-space pages. You created a page on 20 Sep 2018 and uploaded six photos to it. If you click on your first link above, just to the right of the image you'll see "In this image:" with another link shown below it. That link takes you to the actual FSP, and there you'll see the six images. The changes log for the FSP shows the chronology of what you did. Then on 30 Mar 2021 you created a new free-space page and uploaded three photos, all of which appear to me to be duplicates of the 2018 photos. Same scenario, the link to the right will take you to the actual FSP and show you the three photos and the sequence of events.
I would suggest back-pedaling a little bit and trying to get this organized the way you want it. First I'd suggest deleting any of the 2021 photos that actually are duplicates of 2018 photos. Then, if any remain, I would add them to the 2018 FSP (using the 'People & Things in the Image' box under the image). Then remove them from the 2021 page (using the same box). At that point you should have all the photos you have uploaded on the 2018 page, and the 2021 page should be empty. Then I would merge the 2021 page into the 2018 page. (I will see if I can find the instructions for merging FSPs while you are scratching your head over all the above.)
I think your numbering scheme is OK, but just be careful that everything has a unique number. The system will assign its own URLs, but as Julie said, you can rename your photos later to make all that consistent if you wish. If you have more questions or need a hand with some of those steps, post here again and somebody will help.