If the subs needed to be "broken in", then the manufacturer would be sure to make a BOLD NOTE of it. If there was a specific procedure for breaking in the speaker, and warranty was, break-in dependant, then you would most certainly see lots of warnings and the like listed on the owners manual.
There are no such warnings on any JL subwoofers.
It is possible that odler speakers "hit harder" as someone said, but this was not bacause they were "broke in" properly, it was casue they were old. Theoretically, if the spider on the speaker was less restrictive (older), it's possible to get a little more travel out of them based on the same wattage input.