My impression is that so far as their verbal description of their philosophy went, if not its actual use, they claimed that the meaning of any phrase consisted entirely in its impact on experience, and that no other aspect of it is meaningful. This implies that a theory of photons which had photons vanishing as soon as they crossed the horizon of the expanding universe, and a theory which had the photons continuing undetectably onward, had the same meaning.

Logical positivists never reached complete agreement about just what the verificationist criterion entailed. (Their inability to meet their own high standards in this regard was their downfall.) For example, I've read that some of them considered it meaningless to ask whether there's life after death. Whether it is meaningless was apparently a matter of debate among them.

From what I've read, though, the "mainstream" view among them would be that your two theories have different meanings. As I tried to explain in this comment to your OvercomingBias post "No Logical Positivist I", they held that meaningful statements had to be logically reducible to descriptions of possible experience. To quote my earlier comment, "They held that if A is a meaningful (because verifiable) assertion that something happened, and B is likewise, then A & B is meaningful by virtue of being logically analyzable in terms of the meaning of A and B. They would maintain this even if the events asserted in A and B had disjoint light cones, so that you could never experimentally verify them both."

But why take my word for it :)? I'm replying to this comment because I recently came across an article that seems to answer you question. Published in 1931, it was one of the very first articles to present logical positivism to the English-language audience. Here's the reference:

Blumberg and Feigl, "Logical Positivism: A New Movement in European Philosophy", The Journal of Philosophy, Vol. 28, No. 11 (May 21, 1931), pp. 281-296

It's available through JSTOR at the following URL:

http://www.jstor.org/stable/2015437

Here is the relevant excerpt:

It may be objected that certain assertions occur in the sciences which are not verifiable. This objection is based on a confusion as to the meaning of the possibility of verification. That is to say, the impossibility of verification may be (a) purely practical, based on the limitations of our instruments (e.g., propositions concerning the other side of the moon); again, (b) the impossibility may be due to the fact that what is asserted is contrary to the laws of nature accepted at the time (e.g., propositions concerning a perpetuum mobile). Such impossibilities do not prove the propositions meaningless. It is only when theoretically as well as practically there is no possibility of verification (e.g., in the case of propositions which contain undefined terms, contradictions, mixture of logical types) that the proposition is meaningless. Concrete instances of the meaningless assertion are those concerning a Ding-an-sich, Unknowables, realism vs. idealism, the "mental states" of others.

It looks to me like observing events beyond the edge of the observable universe is impossible in the "type (b)" sense. But assertions about such events still have meaning, so it would seem to follow that two theories that make different claims about such events still have different meanings.