;Instead of documentation, I can give personal experience.
I was an altar boy in the late 1950’s, and along with other 6th, 7th and 8th graders, we were kids - meaning there were times we were less than pious.
We used to joke among ourselves as to how long a string of spit the priest had pulled from someone’s tongue at a Mass. It did not occur at every Mass, but it occurred frequently.
NOTE: I did notsay that it is not possible to put the Eucharist on someone’s tongue; I have done it many times over the few years I have been an EMHC, as we have a few people in our parish who prefer to receive on the tongue.
Several differences between now and the 1950’s: Whoever is distributing Communion is normally at eye level with whoever is receiving (and no one has approached me and knelt to receive). The Hosts are larger and thicker than in the 1950’s, which makes it easier to grasp by the near edge. In holding the Host, I and everyone I have received from holds the Host thumb down and pointing finger up when placing it in someone’s mouth; the pastor from my youth had thumb up, pointing finger down as the reverse is awkward when reaching down to someone who is about eye level to your waist, and generally the pointing finger is a bit closer to the enter of the Host, which makes it more likely to come in contact with the tongue.
I have also noted that from the point that the the minister starts to say “Body of Christ” to the point where the Host is either on the tongue or in the hand is markedly slower than in the 1950’s (the pastor was notorious for telling you to move faster if you lagged even a bit - it took literally no more than a second to a second and a half to distribute and be moving to the next communicant.
None of which is to say that if one receives on the tongue that the minister is going to touch the tongue; it depends on a whole lot of minor issues at that moment in time.
But no one is going to draw any spit from your mouth - or even come in contact with the tongue - if they place the Host in your hand. So no one needs a document “deeming safest”. Common sense is all that is needed.
Then, again, Voltaire was right.