With the release of The Unremembered Empire, I do not believe the Space Wolves had a direct hand in destroying those two Legions. A conversation between Guilliman and Faffnr, his Space Wolf executioner: ...
In case anyone is interested, here is the conversation in question:
“What is your duty, pack-leader?’
‘Our duty is what our duty has always been – to do what others will not. To do the unthinkable, if the unthinkable must be thought.’
‘Your reputation as the sanction is well known,’ said Guilliman, ‘and perhaps undeserved. We all serve according to our courage.’
‘Wolves serve beyond that. We are the executioner’s sons.’
‘Who have you come to execute, Faffnr Bludbroder?’
Faffnr hesitated. He reached under his pelt and produced a sheaf of parchment.
‘I see no point hiding it,’ he said, holding the document out. ‘Read for yourself, Jarl Guilliman.’
‘No, tell me in your own words.’
Faffnr kept the parchment extended.
‘Look at it at least. See the seal of the Wolf King, and beside it the sigil of Malcador. Know where this instruction comes from, and the authority it contains.’
Guilliman took the document, unfolded it and studied the marks.
‘Authenticate it if you must,’ said Faffnr.
‘I don’t have to. This is real.’
‘You heard the fate that befell Prospero?’ asked the pack-leader.
‘The Wolves were unleashed to issue sanction to Magnus.’
‘Yes. Not so undeserved a reputation after all, eh?’
Faffnr paused. In the eye slots of his straked and knotted leather hood, his golden eyes blinked once, twice.
‘If one can fall, more can fall. More have fallen. Half have fallen. It has been decreed that a company of Wolves be sent to the hearth-side of every one of the Emperor’s sons, to watch them.’
‘For what?’ asked Guilliman.
‘For signs of treachery, of heresy.’
‘And if such signs become visible?’
‘Then we are to act.’
‘Act?’ asked Guilliman. ‘You’re saying that you are here to watch me? To shadow me? And if you perceive my actions to be in any way untoward, what? You are authorised to enact sanction?’
‘By the Sigillite, so authorised.’
Guilliman laughed. ‘You would… cut my thread?’
‘If needs be. Primarchs are not invincible. Some already sleep upon the red snow.”
Excerpt From: Dan Abnett. “The Unremembered Empire.” iBooks.
I don't see how this is that ambiguous. Faffnr references the rumored duty for which his Legion is so notorious, and Guilliman knocks him down a peg. He's essentially saying, "You're not that special for doing what you claim; we all do what me must, according to our ability." At no point does he dispute the events that give Faffnr cause to consider his Legion legitimate executioners of Primarchs.
At best, I think it can be surmised that Faffnr was not part of the Sanctions against II and XI, and thus can't directly refute Guilliman's claims, but he was present at Prospero and uses it to back his argument.