Great post Ale!
Some more background to justify mixed-singer tandas:
During the late ‘30s and early ‘40s, most orchestras kept two singers “on staff” so to speak at the same time, because they performed so often that it was impractical to have one singer at every single performance. So, for example, in ’42 both Rufino and Podestá sang with Di Sarli; in early ‘43, both Marino and Fiorentino sang with Troilo. They may have even switched off during the same gig on the same night.
So, mixing singers is not that radical. For consistent sound, it’s more important to make sure you’re pulling from the same era, when the orchestra had the same musicians. For example, the musician lineup of D’Arienzo’s orchestra in 1939 was very different from the lineup in 1945, so although Echagüe recorded with the orchestra in both years, the songs sound very different.
I’m also in favor of mixing singers, judiciously. On my tanda blog (https://ddpsfavoritetandas.wordpress.com/) I have quite a few examples of mixed-singer tandas. And just last night, at the Las Puertas Marathon in Albuquerque, I played a mixed-singer Troilo tanda that eveyrone loved: “Cada vez que me recuerdes,” (Fiore), “Garras” & “Cristal” (Marino), and “Gricel” (Fiore) again.