Looking from my books covering Nationalist side (Legion Condor, Aviación Nacional and Aviazione Legionaria) I could not find any claims of downed "Ratas" on the day of 14.6.1938 but yes on the previous day (13.6.) when two Legion Condor pilots (Ewald of 2.J/88 and Schellman of 1.J/88) were credited with a confirmed air victory on I-16.
One unconfirmed claim on I-16 (Mayer of 1.J/88) can be found also on 13.6 but there were not unconfirmed "Ratas" on 14.6.1938 - as shown here:
http://forum.12oclockhigh.net/showth...+Condor+losses
Errors of date in combat reports (and in other sources) are common. Combat reports were written afterwards and were not always so precise in all details like the exact date of the happenings. It was not falsifying deliberately facts but usually just some memorising or writing errors (for example a combat report describing an event of 13.6. may well have been written and dated on 14.6).
One or two day difference in combat reports of different sides are thus not surprising. In this case I´m inclined to believe that the reported I-16 loss is related to one of three (!) German claims on 13.6.1938.
Other well known date and detail differences in Nationalist/Republican sources - otherwise agreeing on what actually may have happened:
Hannes Trautloft´s He 51 was shot down by a Dewoitine fighter on 30.8.1936 according to German sources, but the only known Republican claim to match that is the He 51 claimed by Ramón Puparelli Francia (with Dewoitine fighter) on 2.9.1936.
Italian pilots Ernesto Monico and Castellani were shot down on 30.8.1936 by a flight of three Dewoitine fighters according to Italian/Nationalist sources. Only known Republican claim to match that are two Fiat CR 32 claimed by a patrol of one Hawker Fury (La Calle) and two Ni-52´s (Alonso S. & Dugo) on 31.8.1936.