Flags for limited editions typically include the quantity to be made along with the 'edition number' -- what we refer to as the serial number.
So and LE Flag would say "#___ / 9,500" with the edition number hand printed.
Mukilteo was one of those PLANNED to be a "GLOW" and as such would not have an edition size. But after sculpting and before delivery to dealers, HL bowed to collectors and made it an LE. I believe Fire Island was similar.
If it did not have a hand written serial number it could be an oversight. There is a possibility it could be a paint sample, but very unlikely. It could also be that the hand-written number could have faded off - if the piece was displayed near a window.
Does the one you have have the regular suede-felt bottom or any special paper labels on the bottom?
For any given model, only two paint samples are made. One ships to the factory - and is retained there; the other is held by the company so when the APs come in, they can check the AP painting against the company's paint sample.