When there is no AK, a single "5" makes lots of sense to me.

When I look at the symbol on the right of AK closely, there are actually two symbols.

The one on the top is "4", I would assume this one being a Simson inspection mark (same theory applies to "5").

The one under "4" looks like a crown. It's proabaly AK's inspection mark.

So, when there is no AK, there is no crown. Only a single "5".

Does AK always go with a crown? I don't know.