This statement does not match my experience. With Barry Thornton's Two-Bath developer it is good for 15 rolls and will keep for at least 6 months. If it does go off you will see this in a noticeable change in colour (only experienced this once). You can mix double the amount of Bath B and then process up to 30 rolls by using half for the first 15 rolls and then the second half for the second 15 rolls. The Bath A has the capacity to do this. Naturally, a one shot developer is always fresh and HC110 dilution B is what I always use when teaching people (especially as they are not processing lots of films in a short space of time so the HC110 is both very economical and very long lasting). However, for my own personal work (where I am often photographing an image that includes a courtyard in shadow that has been darkened through bombing and the use of coal to heat apartments and includes newly painted white walls in full sunlight) the two-bath developer gives me more appropriate results.
If you make such statements then you should really do so with a more detailed explanation of why you are making such a comment as 'fact'. For example, a close friend of mine uses Diafine with Tri-X for her street photography and has never had it go bad on her. She mixes it up a new batch every January and discards it at the end of the year. Never ever has she had a problem. What were the circumstances in your case? Was there perhaps contamination? Had you not used it for a number of years, etc?
Bests,
David.
www.dsallen.de