"I'm particularly interested because I have come across accounts of 1400s plate simply shrugging off longbow arrows."

-- that would make the defeat of a French army largely composed of armored men-at-arms by an English army 80% of whom were archers sort of strange, wouldn't it?

See THE GREAT WARBOW by Strickland and Hardy. Testing with replica bows based on the "Mary Rose" examples and carefully duplicated sections of medieval armor has shown:

a) chain mail was very little protection against longbow arrows; not much better than leather.

b) plate was much better, but not invulnerable.

If an arrow hit at an angle, the smooth surfaces of the breastplate, tassets or helm would "glance" it off; the arrow would skip away, and often break.

At 90 degrees, the arrow would penetrate the breastplate (the strongest part of the armor) about half the time, and about half the penetrations would result in serious/incapacitating wounds.

Penetrations went up at close range.

Hits on the joints and weak spots of the armor (armpit, groin, joints, visor, neck) almost always penetrated and almost always did major damage.