That seems reasonable. It's basic Zone System lore, really. Zone testing can be tedious, of course, but in the long run, it saves both time and money.
For the time being you might try intensification.
I'm familiar with two methods. First is selenium toning. In my experience it gives no more than half a grade, but others claim more. Second is chromium intensifier. This is a bleach-and-redevelop process, which can be repeated for even more contrast. I've heard it describes as "risky." It will increase grain size, but for modest enlargements from an LF neg, that isn't significant. Might be worth sacrificing a dud neg, before committing yourself.
I'm guessing now, but sepia toning might work too. I have no more information, but others might.
You haven't mentioned the developer, but if you're using a replenished developer, you might want to check that it is still OK. We have had discussions on the forum previously about certain developers fading away. Slice an exposed neg in half and process one in fresh and the other in the old stuff. Then side-by-side in the neg carrier.