Check out what Simon Galley has to say about the latent image characteristics of Pan-F+:

"Latent image stability, a real issue on papers and films, both colour and monochrome some are better than others but by and large they are all amazingly stable especially when you consider the LI performance of 50 years ago. If we talk about PAN F + when the ( all new ) plus emulsions were introduced, one major improvement was latent image stability. I should know, but I don't where PAN F + comes in LI performance compared to our other film emulsions but I will speak to our technical service, they will advise me and I will let you know in the next day or so. "....

I've long had the idea that Pan-F had an issue in this regard, but perhaps not.