> If you get a new certificate issued from the X3 intermediate that chains to the ISRG root, but you serve the old, cross-signed X3 intermediate in the TLS hand

> If you get a new certificate issued from the X3 intermediate that chains to the ISRG root, but you serve the old, cross-signed X3 intermediate in the TLS handshake, the connection will still work (* for now, keep reading). Seems to suggest "yes"