What is the deal with 道地 versus 地道?

Various sources seem to have conflicting/confusing information about this. As far as I can tell:

* 地道 dìdào with a 4th tone on second syllable means "tunnel". * 地道 dìdao with a neutral tone on second syllable means "authentic". * 道地 is a variant. It only means "authentic".

Is this correct?

The Pleco PLC the entry is very confusing and seems to say it can also mean "tunnel" but other sources disagree.

Words that are written identically and distinguished by tone are very unusual, in practice I assume you have to rely on context.