The issue is… That says T9. Which is the prototype as seen above.
As we know only one T9 was built, I think we can safely assume it means T9E1s (aka M22s).
The wiki article on the Littlejohn suggests this is not true - that the adaptor could be easily removed if HE was going to be required for example.
However it also includes a couple of interesting things:
1/ Americans testing it in 1943 found the adaptor distorted after a few shots; and
2/ When British a/c crews found the AP ammo for the adaptor worked perfectly will without it, and was superior to standard AP, they just used it without the adaptor fitted!!
Likely point 2 above - it had a tungsten core so defectively HVAP
The Americans may not have classified it as the M22 when this document was created. The Locust was originally built specifically for the British as a replacement for Tetrarch.