score:4
The RMV website has an option to indicate the zones in which the day pass is valid. To get this information, search for a specific connection, click on the >
the open connection details, then click on Tarif, then on Tageskarten, and then on the >
next to the type of Tageskarte under consideration. A ticket from the Frankfurter Straße in Offenbach to the Frankfurter Straße in Langen (direct route) is valid in tariff zones 3500, 3600, 5000, 5090, 2645, 4089, 6649, and 6664:
One can then also click on Freigegebene Städte/Gemeinden for more information, including a full list of municipalities and cities where it is valid:
The conclusion in this specific case is that a Tageskarte with Preisstufe 4 is indeed valid in the entire A-areas 3500 and 3600, including Offenbach, Dreieich (of which Sprendlingen is a part), Langen, Dietzenbach, and even all the way to Seligenstadt and Frankfurt including the airport. However, if one searches only to the far north of Langen, then the Tageskarte is not valid in the entire A-Zone, because it is only Preisstufe 3:
In this case, 3550 is not listed. For the journey described in the question, one has the choice: