Don't give up.
But if you can figure out a way to reliably test the behavior of a single litre
of 48 hour old 1+3 diluted D76 without either using it up by developing a whole roll of film to do the test or employing a step wedge, a clip, and a densitometer, I'll be happy to change the recommendation
OK Matt you've persuaded me- I won't give up
Firstly are you saying the exposed leader test for testing developer is useless? If so then there is no point in my continuing and we can just "beg to differ"
However I will give you my reasoning for my endorsing the testing of the 48 hr old 1+1 D76 as a "nothing to lose" strategy
The time for a 1+1 fresh dilution to develop film X is a known so using that time the OP uses the short exposed leader and develops for that time. This can be done in the daylight and with relatively little of the diluted 48hr old 1L of D76
The leader being exposed should turn a deep black i.e. should look like a leader developed in fresh 1+1 D76. OK how does he judge this black if he has not kept any previously developed leaders from fresh 1+1 or indeed fresh full strength stock with which to compare?
That does give him more of a problem than comparison with a leader developed in fresh developer although it is largely the same problem I posed to Don Heisz who described a test for unknown film which was wait until it goes black and double the time. It involves some judgement as to what "black"is
When I test Xtol stored in a winebag for a while I use the incandescent clear bulb filament test If I can see the filament as a clear orange strand then I found that the developer was still giving me OK negatives from which I could see little or no difference from the Xtol that was new, The same black leader give me a very dark looking outside scene in which there was little detail when held up to a window
On the above Xtol test I will now say that I became a little wary of using it when the stock had turned from water white to the palest of straw colour and I mentioned this in a thread to which you replied. I mentioned that I thought that the leader in that test had allowed the filament to appear slightly brighter and it was you, if I recall correctly that said you thought the Xtol to be OK but to be on the safe side I should develop the film for a bit longer
So yes some judgement is called for on the part of the OP but it seems to me that if the 48 hr 1+1 D76 gives him a slightly less black leader then if my experience is anything to go by he will still have negatives that are OK to darkroom print or scan and print and he will lose nothing if he adds a bit on to the recommended development time
Will he have the prefect negative or the perfect print, possibly not as indeed neither might I have gotten the perfect negative using older Xtol but I did get perfectly usable negatives that gave me usable prints that I am happy with
If I may say so this whole unbridgeable divide between the "dumpers" and "testers" seems to be less about the testers inviting the OP to pursue a course that inevitably leads to almost certain disaster and more about avoiding anything which might be sub optimal in the slightest. That is a discussion that will always generate 2 opposed parties and on which there is no end except to agree to differ.
I cannot speak for the other "testing" advocates but in making my suggestion I was driven by what I thought was a desire by the OP to find out if there was any way to check if his 48hr dilution was OK
I had assumed that if he was 100% risk averse then he might have simply dumped the 48hr 1+1 dilution and never bothered to ask the question. Believing he wanted to find out if there was any chance his liquid was usable to the extent of giving his negatives a real fighting chance I advocated leader testing as it had worked for me
I interpreted( may be wrongly) from his last post that he had decided against testing and of course by then and certainly by now his several days older 1+1 D76 becomes more problematical in terms of its efficacy
As long as I can remember I will try on the next occasion when a similar thread arises to ask how important it is for the OP to be 100% sure of doing everything to ensure there is not even the slightest risk to the film
If the reply is that a 100% certainty of perfectly developed negs is required then I shall at least point out that 48hr old diluted D76 may carry some risks