To summarize J-STD-001, anything with a gold thickness of greater than flash gold (<10 micro-inches) must be gold washed in surface mount applications.  As for through-hole applications, the standard is higher in terms of thickness, but the problem of gold embrittlement must be assessed.  Even in surface mount applications, the issue is not in achieving a solder connection as hard gold (up to 18 micro-inches) can be soldered to fairly well, it is the concern of gold embrittlement leading to pre-mature joint fatigue and failure.  Hard gold is tricky as the time above liquidus
The reason for this is that gold does not alloy well, rather it dissolves into the connection and/or creates AuSn nodules which weaken the joint integrity.
I suggest contacting Leo Lambert of EPTAC ([log in to unmask]) who is one of the pre-eminent sources on gold embrittlement.  Also, there are several resources on their webpage.  Leo is the IPC Expert for much of the Northeast US.

NOTE1: If it is for a space application, gold wash is mandated.
NOTE2: Through-hole (bulk solder) connections typical yield a much lower gold percentage but, because the solder time is much shorter, the degree of gold diffusion is less meaning that the gold percentage left in the critical IMC region is much more than from SMT where the longer time above liquidus aids in diffusion of the gold.  This shows up most significantly in the feather regions of the connection where the amount of solder available for diffusion is the least.