Scott, I don't know what the BIA says about this issue. All I know is what works and doesn't work around here.
Rusting lintels are a big issue in our area. Lintel replacement costs big money. The problems we have here is that a mortar joint between the brick and lintel never stays tight for long. Essentially, one is attempting to bond (seal) two dissimilar materials, which almost always leads to failure. The joint fails, driving rain/snow get into the joint, lay on the lintel and rust it out.
Caulk on the other hand will bond to both materials. The caulk will also flex and move as the steel/brick moves with weather changes, thereby staying sealed and prolonging lintel life.
In older construction here, water needing to come out of the wall at the lintel hasn't been an issue that I know of.
In new construction masons usually are putting weep holes in a row above the lintel. The lintel/brick joint is then caulked.
Most guys are using a butyl or solar seal, some urethane.
There are some still mortaring the lintel/brick joint but it is not a popular method anymore here.

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