I mean, presumably SCTs in the certificates themselves were from the CA submitting the precertificates itself. So because Let's Encrypt submits their final certificates to CT logs as well (which not all CAs do), one could crawl through all those and get the list of what logs were used, or at least what logs can answer quickly enough to get their SCTs embedded.
A lot of work for not really a lot of benefit, though, they basically just submit everything everywhere. 