I am reading about randomization techniques and have a curiosity: for multicenter trials, if one has a bunch of sites, each with varying sample sizes (for example, one site has only 4 participants enrolled, a few sites have no participants so far, another has 59, another has 68, another has 7 and so on), is it possible to use blocked randomization within each site to randomize the existing participants in 1:1 ratio to either group A or B?

For 59 participants, if you want a block of size 6, I guess you could do 9 blocks but then you'd have 5 participants left over. Is it customary to do block randomization for the 54 participants and then just simple randomization for the remaining 5? Or does it not make sense at all in such a situation to even bother with block randomization?

I have found plenty of examples but they all seem to assume that you have the same sample size (and furthermore, that sample size is an even number) for each site..

Thank you kindly for any advice/resources you can provide about this.