I'm always surprised to find practical men making heavy weather of Best Before, Use By, and Expiry Dates etc. They're broad hints rather than time-bombs. Unlikely that the shelf-life of cutting fluid is critical.
With food and drugs suppliers are required by law to think carefully about how long their product is safe and how long it is effective. (You don't want to take drugs that have decomposed, or eat rotten food. 'Best Before' typically indicates that food is still edible, but may not taste nice, or has an unpleasant texture.)
Quite a few chemicals 'go off' to some degree or other. Leave petrol in a can for a few years and you will likely find light fractions have escaped past the seal leaving fuel that an engine will find hard to start. That's annoying, but leaving Dynamite in a warm hut for 20 years could be fatal.
Many chemical products like Rocol Cleancut are carefully formulated mixtures that can and do age. Also, I notice a number of chaps mention owning 'Rocol' for many years without specifying which of several Rocol cutting agents they have. Without that information all bets are off! RTD Cleancut is not the same as RTD Compound. Is the difference significant? We don't know.
Some customers demand consistent high-performance from products like cutting fluids. What's acceptable in a jobbing workshop might be an expensive mistake on a busy machine centre. Others, like the military, insist on almost everything being fully documented and this often includes a shelf-life assuming worst case storage conditions. It's not worth compromising military operations by penny-pinching.
My advice is use your loaf. Don't drink sour milk even within the best before date. Cutting fluid will likely produce reasonable results long after it's expired on paper. Try it and see.
Bit of a minefield for which it's all too easy to blame Brussels. I'm expecting fireworks next year when those looking forward to fixing pet Euro peeves like this discover leaving Europe makes no difference to them whatever. May be wrong – this time next year, we'll know for sure.
Dave