Reply to Justin B.
John R.

Justin asks why Eriol was able to step foot in Aman in The Lost Tales.

The simplest explanation is usually the correct one. Remember that Tolkien essentially abandoned his early work re Eriol and the House of Lost Play business in favor of the Silmarillion and later the Lord of the Rings. Even though Tolkien spent years on the latter, there are still inconsistencies. So, my answer to Justin's question is that Tolkien likely never fully developed his Eriol story to his own satisfaction and did not get around to addressing conflicts, discontinuities, etc.