N_Cook wrote:

Where would they have come from ? some batch of other double tetrodes and
markings removed ? all Chinese script so scrubbed off ?

Rumors say, that some tubes from me-too-ers have been remarked
to appear as from a high-quality producer.

4 presumably ECC83 in a Laney (not originals) all test bad C/H leakage and
bad/ low or marginally good gain.

To be certain, you have to eliminate the "presumably"
(by measurement?).

Not a trace of any marking , as low power
valves, presumably no marking originally. They look like any other ECC83, no
bad cut metal/ broken mica or any other indication of bad manufacture.

Some ink seems to soften over time, so that even touching/handling
rubs the marking off.

Regards,
H.