(This was a late-night thought, the basic premise of which is that Wadi el-Hol might more squarely fit the after-Sinaitic and before-Arabian writing period - placing it anywhere from possibly around 1400 to 1200 BC).
I think, given what I feel to be the high consistency of my translation of Wadi el-Hol both internal to Semitic alphabetic scripts but also to our knowledge of the specific use of that area [of Wadi el-Hol] that the alphabetic inscriptions there are likely from a range closer to 1400-1200 BC rather than 1800 BC.
In fact, the presence of this distinct ḥ, arguably continuous with the Arabian (12th-9th centuries) ḥ probably should have indicated this possibility far earlier on. Whereas I have argued, and will continue to do so, that a fish-ḥ is present in Sinai, this isn't found outside and neither is another (or arguably a) distinct ḥ. However, that same ḥ does occur in Sinai, Proto-Canaanite, Phoenician [and Greek and Latin E] as an h. The confusion of an apparently less distinct Northern Semitic ḥ in contrast to the continuing distinction in Ethiopic, Arabian etcetera is one possible mode of transmission (a sort of Shibboleth confusion probably of similar names - hawy and ḥawy, perhaps).
Sinai, which can be more reliably placed within a range of 1700-1550 BC, squarely within the Hyksos and Intermediate periods, attests to none of this. Neither do anomalous probably South Egyptian inscriptions purchased by Petrie in the early 20th century. The one anthropomorphic h-letter is almost certainly pronominal and hence a continuation of the h from Sinai. This is highly anomalous given Wadi el-Hol. Moreover, these same inscriptions seem to foreshadow later-Arabian paleography with specific regard to S1 and Z. In fairness, the one inscription [Thebes 1] that may contain an h is highly dissimilar to the other two [Thebes 4 and 6], which are likely in similar alphabets or the same one.
So it may be the case that Wadi el-Hol is one point of transmission from North to South and eventually Arabia, but it is likely not the earliest one - if one buys the issue of ḥ and h [or understands what I'm saying - get back to me on that]. However, the same otherwise seemingly unique Wadi el-Hol h, one-arm-up and one-arm-down person, might be attested in an anomalous Yemeni inscription called Jamme 863 - which also attests the Arabian worshiping ḥ but upside down. It is an anomalous inscription that Jamme and Albright felt was also archaic - and it may be on the former rock-wall of a structure.
Moreover, the same one-arm-up and one-arm-down person may also have become the Ugaritic alphabet's ḥ, its h the more commonly held Proto-Canaanite h. That alphabet evolved sometime between 1200 and 1150 BC in Coastal Syria. It also held an abecedary in the South Semitic [Arabian] order. This connection is unusual, and it suggests a written connection of yet unknown character. It does, however, open the possibility for, essentially, backdoor transmission of the Proto-Sinaitic or Proto-Canaanite alphabet to South Arabia by that time [including the possibility it was transmitted through Ugarit].
But if one actually goes back over these highly anomalous inscriptions, a clearer likely path develops: Sinai Peninsula - 1700-1550 BC, Canaan - 1400-1300 BC, South Egypt Petrie - (perhaps) 1400-1300 BC, Yemen (perhaps) 1300-1200 BC, Coastal Syria 1200-1150 BC. The core question is whether the evidence for the dating of Wadi el-Hol to 1800 (or 1800-1700 or whatever) BC is strong - particularly given it is based on an unknown language and no agreed-upon translation, nor any physical evidence. Based on my translation, I had always been perplexed at how the Wandering Goddess story could have been present by 1800 BC. However at the beginning of the New Kingdom, there is now a philologically consistent story.
It may be the case that the collapse of the Hyksos, random scribes were pushed primarily across Sinai into Palestine. However, some no doubt remained in Egypt and/or as the Syrio-Palestinian royal and aristocratic entourages returned to regular tutelage, it spread that way [possibly also]. Hiring Canaanite shamans was not unknown, so some scribes from the Sinaitic period might have found purpose there. Two of the Petrie Theban inscriptions are likely invocations - one of which is a curse; another, I have argued with increasing personal skepticism may be a star chart. The third is very unclear but is possibly an invocation to Set.
Having said all that, the Wadi el-Hol inscriptions are not a hoax. However, they are likely not as old as has been commonly thought. They do, however, represent one of the most important discoveries in the history of the study of the alphabet - in that they likely do reflect the earliest common link between Sinai and Arabia. They are also definitive evidence for the nomadic, almost certainly Syrian, use of the alphabet (probably the earliest definitive use) in that they were clearly carved in transit - at the site of a Hathoric shrine or temple on a road between Hu and Thebes. And the timing explains why Athtar's name is written with an `ayin that seems far more at home in Ugaritic than Proto-Sinaitic.