* In 2015, at 66 (FRA) I filed a restricted application for SS, opting for a small spousal benefit on my current spouse's record, and deferring my own benefits till I'm 70.
* I've received a small Belgian SS pension since 2014 (age 65), ranging from $375 to $410 a month depending on the exchange rate. (10 years of work in Belgium with mandatory SS contributions, followed by 14 in the US with mandatory SS contributions -- leaving me with sufficient credits in both countries so that the totalization agreement with Belgium does not apply to me or make the WEP moot.)
* My current spousal benefits are NOT subject to WEP. Would this be true as well of derivative benefits from a former spouse (who is not himself subject to WEP or GPO)?
* Even at 50%, derivative benefits from my former spouse have the potential to be considerably higher than my own future benefits at age 70. So I would like to look at this option if I meet the eligibility requirements for derivative as opposed to spousal benefits. Not sure, however, how the WEP would factor in.
First off, if you're remarried you can't draw divorced spousal benefits while your ex-spouse is alive. You could, however, potentially qualify for surviving divorced spousal benefits if you remarried after age 60.
The windfall elimination provision (WEP) does not affect spousal, divorced spousal, widow(er) or surviving divorced spouse's benefits. The government pension offset (GPO) provision can affect those categories of benefits, but foreign pensions like your Belgian pension are not considered as government pensions for purposes of GPO.
So, it sounds like you have no worries with GPO, but the WEP provision will likely reduce the rate of Social Security retirement benefits payable if and when you file on your own record. There is a WEP guarantee provision, which may apply in your case, that limits the amount of the reduction to no more than basically 50% of the amount of the non-covered pension. For more information on WEP and how it affects benefits, refer to the following pamphlet: https://www.ssa.gov/pubs/EN-05-10045.pdf.
By the way, the maximization software available on this website is programmed to handle both WEP and GPO, so you may want to use it in order to decide on your best course of action.