Well, it did, and now I'm confused all over again.
The credit in my account for £1.34 dated 27th August wasn't for the half-price charging session that day at all, as I thought it was. It was actually for the 18th August "free hour". This is more than I had anticipated, and does indeed more than compensate for the solar export I lost in that time. So I must have dropped a stitch somewhere, but now I have no idea how they work it out. I mean, given that I had to use all the solar first before I drew anything from the grid, how come?
Still no word on the half-price car charging session.