I haven't read The Night Watch - I loved The Paying Guests as well though! Eventually I'll get around to reading all Sarah Waters' books (Sapphic historical fiction by a Welsh author - how can I resist? Lol.)
I was surprised - given how much I'd heard about this book being about Lesbians - that I hadn't heard anything about the gender expression at all. Nan so clearly discusses her experiences of feeling 'between' genders, at length, and switches pronouns, etc. - and I was like... why has no-one mentioned this when they rec. this book online? I've seen this book rec'd by so many Sapphic bloggers, BookTubers, etc., and none of them mentioned it - it's almost a disservice to how complex the book actually is.