Gallery card different validation results depending on code


The documentation here is quite clear that the four image tags are required:

However, I get different validation results leading me to question the exact requirements. Must we supply four images? Or can we supply 1, 2 or 3 images?

In the validator, given this markup:

	<meta name="twitter:image0:src" content="">

I get this result:

Aside from the red circle, all indications are that the validation passed.

However, given this:

	<meta name="twitter:image0:src" content="">
	<meta name="twitter:image1:src" content="">
	<meta name="twitter:image2:src" content="">
	<meta name="twitter:image3:src" content="">

I will get errors saying that image1, image2 and image 3 are required.

So the simple question is: Which is correct? Is there a bug in the validator that should be explicitly failing completely absent (rather than empty content) tags? Or is it acceptable to specify < 4 images as long as there are < 4 tags?

I know, of course, with only one image there is a different card for that, this is more of an example than anything.

Thank you.