I keep them in order of the emperors reign so when I get a new one I have to take out all the others after a new emperor or empress and make room for the new one to be placed. Sometimes I leave a empty for a cheap one I know I will buy in the future but sometimes that isnt the case.
I had a problem with this as well. Add a new Vespasian from early in his reign, and redo all the others. I finally started leaving 4 or 5 blanks on each page to fill in, and I don't have to reshuffle now until I add lots of new additions in a given area.
It's not a problem if you enjoy handling your coins. Seriously. I used to fill my trays in a similar manner with no blanks, accumulate a group of coins through purchases over several months, and then have the unmitigated pleasure of having to rearrange all my trays from start to end to fit in the
new coins. Sometimes when I'd finish I'd
still have a coin left over with no space for it, or a blank with no coin. Perhaps unconsciously I made the odd deliberate error to have the fun of rearranging a second time.
Seriously though, there are all sorts of practical means getting around the 'problem', if you regard it as a problem (which it perhaps isn't). Aside from leaving a few blanks on each tray or page, if you think that looks untidy then you can arrange your coins in groups (Julio-Claudians, Flavians,
Hadrian to
Commodus etc) and at the end of each group chance will ensure you've a few blanks; in that way there is less rearranging to do, whilst
still essentially keeping each page full.
I've slimmed my
collection in recent years, and now have about 20 trays of coins which I operate on a strict one-in one-out regime. When I add a coin to a tray, it must be at least better than the worst coin currently in the tray (worse, considering
rarity as well as condition). Then I remove the 'worse' coin which gets relegated to my study box, and eventually sold. In that way I don't really ever need to do a full rearrangement, just one tray. But to be honest, a full rearrangement is so much fun.