Just marshalling people's opinions leads nowhere, unfortunately: we have to know ON WHAT EVIDENCE THOSE OPINIONS ARE BASED!
For
Lucilla, I believe dates are deduced from the accounts of her conspiracy in Dio, the SHA, and
Herodian: where do those accounts occur in the narratives and what datable details are mentioned.
From Kaiser-Raiss, Münzprägung
des Commodus, pp. 17-21: Lucilla's conspiracy usually dated to 182 or 183 on the assumption that
Commodus adopted the title Pius in commemoration of its suppression, but the connection between
PIVS and the conspiracy is not an attested fact.
K-R suggests instead a date at the end of 181, on the basis of the
SECVRITAS PVBLICA type that appears then on
aurei, and the fifth
largesse distributed by
Commodus early in 182, following with surprising rapidity on
his third in 180 (accession) and
his fourth in 181 (return to
Rome?).
K-R's date of late 181 for the conspiracy is followed by
Kienast, Kaisertabelle, 1990 edition, pp. 145-7.
As to
Crispina, I think the problem is that she is named in inscriptions much later than her presumed fall early in the reign. Moreover her brother was
consul in 187, unlikely if
his sister
had already fallen and been executed and
had her memory condemned!
Kienast Kaisertabelle p. 150 dates her fall to Fall 192, on the basis of the
inscription ILS 405 as interpreted by Grosso.
Unfortunately I have never been able to acquire copies of the reprint of
ILS or Grosso's book on
Commodus. Lars, can you send me a scan of that article on the
inscription from Sabratha?
When do the coinages of
Lucilla and
Crispina end? That is a problem that should be soluble on numismatic evidence, but no one yet has assembled the necessary material to see what emerges!