FBI NICS will discontinue extending courtesy instant BCGs to the state of WA for long guns other than SARs (bolt/lever/pump/single-shot rifles, and shotguns) and firearms categorized as "other" (which includes frames/receivers). Starting July 1, 2020, buyers of those long guns & frames will have their BCGs run by their local LEA, which means a mandatory wait period, at a minimum. I don't think they will require SAR training certificates or incur the $18 SAR tax/fee at time of transfer, since they still aren't SARs. But you definitely won't be able to walk out of the store with it same-day, and your serial # will most likely end up registered with DOL.

In other words, buy your lowers, Glock frames, and any other frames/receivers you want before that date.