Did anyone conceive a girl when OPK was still negative?

Timing doesn't work, so you can get a boy or a girl every fertile day. Scientists using modern technology have even gone back and used Dr. Shettles' own data to prove it doesn't work; when they correctly pinpointed ovulation using the information we have here and now (instead of just assuming people ovulated CD 14) they found about 50-50 boys and girls conceived every cycle day using Shettles' data in addition to data compiled with modern technology. I get that you got a boy at positive OPK before, but that was not because of that BD timing, but in spite of it.

All that having been said it's of course fine to include timing if you want to (just be sure you're swaying in other ways, and only do one attempt). If you're under, say, 38ish or so (I'd make this limit more like 36 if you want more than one additional kiddo) and want to give a 4 day cutoff a whirl, why not? (If you're 38+ or 36+ and you want 2-3 more kids, I'd not use this method for longer than a month as it will lower odds of conception too far, wasting precious time in your fertile window.) Just don't stay "married" to it forever; what people sometimes do is get so fixated on methods that really cut conception and do not work, that they end up dropping things that DO work and keeping the thing that doesn't, in order to boost chances of conception.

The odds of conception 4 days before O are roughly 1 in 1000. Not impossible, but a longshot, and most of the people who conceive with this timing ovulated sooner than they thought they did.

To answer your question, I got three of my boys with longer cutoffs. I can't say how long as this was before I was savvy about all this, but my first boy I had sex the day after my period ended (CD 7 at the latest) and was SHOCKED to come up pregnant. Obviously I ovulated early, but it would have had to be at least a 3-4 day cutoff. I've never had a super short cycle either before or since, so I doubt I Oed any sooner than CD 11. My second boy, we were trying and then my husband changed his mind several days before O. We'd only had sex twice and both of them were prior to CD 10 though I don't remember which days specifically. I thought I had absolutely no chance that month. I had very regular cycles, and again, while I likely Oed early, I didn't usually ovulate early so it was a solid cutoff with him. And my third boy I was trying for Shettles, super regular cycle again, and had sex at least 3 1/2 days before I expected to O. My husband wasn't even home when I ovulated, and by that point I was pretty good at knowing when O happened so it really was a long cutoff, but I could have erred a day or so because my O symptoms sometimes take a day or two after O to go away.

My point is not to say that cutoffs sway blue, because timing doesn't sway. Simply to point out that it is possible to conceive with longer cutoffs and I hope that's the case for you. Pink dust headed your way.