In the two getContext() tables https://html.spec.whatwg.org/#dom-canvas-getcontext and https://html.spec.whatwg.org/#dom-offscreencanvas-getcontext, the entries where the contextID matches the context mode are not worded very clearly:
Return the same object as was returned the last time the method was invoked with this same first argument
These entries should be reworded so that the state is explicit.