Legal definition of LOA that builders must use:
20 CFR 701.502 (b)(1)
“Length” means a straight line measurement of the overall length from the foremost part of the vessel to the aftmost part of the vessel, measured parallel to the center line. The measurement must be from end to end over the deck, excluding sheer. Bow sprits, bumpkins, rudders, outboard motor brackets, handles, and other similar fittings, attachments, and extensions are not included in the measurement.
Swim platforms that are integral to the hull (part of the hull mold) are included. Swim platforms that are bolted onto the stern are not.
However, Harbormasters only want to know how many feet of dock space they can charge you for, so they can--and do!--include anchors, pulpits swim platforms NOT integral to the hull and anything else hanging off either end of your boat.