This isn't accurate.
"To count, your journey must be 75 miles or more travelled between two stations, using a ticket valid for travel on Avanti West Coast services. It can be completely via Avanti West Coast or for just a stage of your full journey – but this stage must be 75 miles or more."
It can have connections, but the Avanti leg(s) must be 75 miles+
I stand corrected if there has been a change in policy since last September when I queried my lack of credits on a few tickets. At the time the qualification policy was worded slightly differently, (which I've just validated via Wayback Machine) but didn't flag journeys including other operators.
Here is the response from Avanti last September when I queried getting no credits on a number of Leyland - London tickets when I questioned their first rejection of my missing credits:
"Dear Mr RAPC
Thank you for your email regarding your claim about your recent journeys not crediting. I understand that you have questioned why your tickets from Leyland to London Euston have not credited to your account and why these are considered to be ineligible.
These are not qualifying because part of your full journey is on a service operated by another company. A qualifying journey must be completed on an Avanti operated service or services, without any other operators on a ticket purchased via the Avanti website or app.
I can see how this may not be clear on the website and I have passed on your feedback to the relevant team. By way of a small apology, I have applied a free hot drink to your account, which can be redeemed in our onboard shop next time you travel.
Thanks you (sic) for contacting the Club Avanti team.
Kind regards
xxx xxx"
Sounds like they've opened it up to include partners (as I believe was initially intended) in the past months, which is a good thing as the previous policy was not customer friendly.