The excellent descriptions provided are for tapping blind holes all the way to the bottom of the hold. But you say you "But no issue, as I am not tapping any blind holes."
I am no expert but can think of two situations where just the one-line tap would be all you need.
What appears to be your case where the hole goes all the way thru ... i.e. no bottom. There is not benefit to using anything other than the first tap. Just run the tap in so the main body of threads have gone thru the hole [you will feel when it is no longer cutting and simply screwing it itself into the plate]. I then clean the crap out of the hand tap with a brush and then back it out of the hole. A gun or spiral tap may not have as much crap in it as a hand tap so the step could be avoided, and I am sure there have been a bazillion holes tapped without bothering to clean the tap before unscrewing it so I am probably just wasting my time there.
The other situation, which does not appear to be yours, is where you do have a blind hole but it is deeper than needed for secure attachment. I would then just run the first tap in far enough to provide sufficient threads to hold things together. Cutting threads all the way to the bottom of the hole doesn't add any value assuming the length of the bolt is appropriately sized ... as in long enough to hold things together yet not so long that it will end up in the uncut portion of the hole.
Of course if you are working on an airplane or space vehicle please ignore everything that I have suggested.
And as Vinny pointed out, for 70 holes some type of machine would be great ... be it a drill press with a tapping head or robust variable speed hand drill with a block or some other device to ensure that the tap will start in the hole correctly. A hand drill without an alignment device will be a disaster.
Which does beg the question ... how did you put 70 holes into what ever it is in the first place? But I digress.
And as I said, I am no expert so any corrections or concerns about what I said would welcome.
I am no expert but can think of two situations where just the one-line tap would be all you need.
What appears to be your case where the hole goes all the way thru ... i.e. no bottom. There is not benefit to using anything other than the first tap. Just run the tap in so the main body of threads have gone thru the hole [you will feel when it is no longer cutting and simply screwing it itself into the plate]. I then clean the crap out of the hand tap with a brush and then back it out of the hole. A gun or spiral tap may not have as much crap in it as a hand tap so the step could be avoided, and I am sure there have been a bazillion holes tapped without bothering to clean the tap before unscrewing it so I am probably just wasting my time there.
The other situation, which does not appear to be yours, is where you do have a blind hole but it is deeper than needed for secure attachment. I would then just run the first tap in far enough to provide sufficient threads to hold things together. Cutting threads all the way to the bottom of the hole doesn't add any value assuming the length of the bolt is appropriately sized ... as in long enough to hold things together yet not so long that it will end up in the uncut portion of the hole.
Of course if you are working on an airplane or space vehicle please ignore everything that I have suggested.
And as Vinny pointed out, for 70 holes some type of machine would be great ... be it a drill press with a tapping head or robust variable speed hand drill with a block or some other device to ensure that the tap will start in the hole correctly. A hand drill without an alignment device will be a disaster.
Which does beg the question ... how did you put 70 holes into what ever it is in the first place? But I digress.
And as I said, I am no expert so any corrections or concerns about what I said would welcome.