I suspect pressed - unlikely that all those mitres would be cut, running as they do around the curve of the base. You should be able to feel the difference between the two processes - if in doubt use a small lens to look for the remains of grinding marks within the mitres - factories were very good at removing mould seams by means of fire polishing.
You don't mention the extent of wear, if any, which might help to indicate age - but as a guesstimate could be anywhere in the first half of the C20. If it were earlier you should have substantial wear.
The cross in the centre of the relief diamond is a nod to earlier cutting designs, where this feature was called, rather obviously, a cross-cut diamond.
The diamonds aren't of course in relief, it's just that visually they appear so.
Lids on pickles needed to be vinegar fumes proof, so these ground stopper lids/bodies were paired and matched to provide a very good fit. The positioning of your matching Nos. is typical.