David Reigle wrote:
Vālmīki’s first śloka, however, is being quoted in this kāṇḍa, to explain how the śloka meter arose. It is not part of this kāṇḍa's narrative as such. So its language is not necessarily the language of the rest of this kāṇḍa, and its age would be independent of the age of this kāṇḍa.
 
Looking at the distribution and locations of "vai" and "ha" in Ramayana book 1.

Chapter 1 has the most occurances of "ha" in the Late Epic expected location at paada end,  6 times.  with no occurances in Vedic expected position (of second word in sentence or anywhere else). vai does not occur in chapter 1.

Chapter 2 which describes the creation of shloka metre incident is more ambiguous.  "ha" occurs in verse 8 at Vedic expected position (second word in sentence) and once in non-vedic expected position but not at paada end in verse 19.  And "ha" occurs once in Late Epic expected position at paada end in verse 20.

But what surprises me is that the occurance of "ha" is so irregular since its use in the Ramayana (with only one exception) is as a metrical filler at paada end. Chapter 1 having 6 occurances of "ha" at paada end but with many chapters not having "ha" at all. 

"ha" does not occur in chapters 3 thru 8, 11, 14, 15, 16, 18, 19, 20, 21, 23 thru 33, 36, 37, 39 thru 42, 44, 46, 47, 49, 50, 52, 54, 55, 56, 57, 59, 63, 64, 67, 69, 71, 72, 74 and 76

Thanks,
Harry Spier