Not sure why, but this episode didn't work for me.
I don't think it was how far back it went, as the Matthew Pinsent episode went back further - connecting him to royalty, Charlemagne, Jesus and God, and that was OK.
Maybe by parachuting Celia in to the 17th century, without any confirmation of her link (on-screen at least) made it feel more like a history show than WDYTYA.
This series has been very contrasting - too many episodes going back just one or two generations, often culminating at WW1 (important though this era is), then this one that jumps straight back over 300 years.
Nevermind, still two more episodes to redeem it.