Hello Anne.
Would agree with you regarding the cancellation 'slashes' on this weight, I can't think of any other rational reason why the marks should be defaced so strikingly - obviously the authorities felt strongly that pieces needed to be de-commissioned in a very formal way. Worried perhaps that re-use in an uncontrolled way might endanger the standards of the world of commerce. Just shows how times have changed.
Turning to the matter of the Uniform Verification Nos. - glad we agree on this also, makes me feel I'm not barking up the wrong tree - but.......am I correct in saying this is only half the story. Reading the details of your link, I would understand it that the other marks on my weight - including Keith's reference to City of London and Guild Company Hallmarks - would be termed the pre 1879 Verification Marks - to which the text refers.
P.S. Next up, when I get time, is a pewter tankard with Chinese/Japanese touch marks - not remotely old I'm sure.