David,
Work on the basis that the markings give enough information to trace each component back to source, so that any defects/defective parts can be traced by batch to the originating factory or filling station.
Primer markings have the date/manufacturer/type (eg No.1 or No.11 in the case of a 25-pdr)/date of manufacture, and a second set giving the filling station/date of filling/batch number.
Cart case is similar. At each refill, the first 'F' is struck out, and another F stamped adjacent. As Adrian said, CR is not applicable to the 25-pdr as it is a separate (not a fixed) round where the charge weight can be varied at the gun. AT rounds are 'fixed' and cannot be varied, hence any reduction in charge weight is done at the factory/filling station.
Cart cases are returnable stores, ie 'produce' where the spent primer is removed, the case cleaned, and then measured for wall thickness/length/ before annealing, full length resize in a die, length trimmed, checked for imperfections, then sent off to the filling station (or scrapped). With a 25-pdr, there was such a variety of charge weights that the stress on a cart case could vary greatly, so it was worth the trouble to return and if within tolerance, re-use.
Mike
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