The documentation states:
'Layr', 'Lr16' and 'Lr32' start at See Layer info. NOTE: The length of the section may already be known.)
While this is not very clearly written, it appears in practice that, when encountering an 'Lr16' block in the Additional Layer Information - after reading the 4-byte signature, 4-byte code, and 4-or-8-byte length - you should pretend you've just finished reading the 4-or-8-byte length of a Layer Info block, which previously indicated a length of zero earlier in the file. Continue using the new length value instead, and proceed to read the next two bytes, which will be the layer count, followed by layer records, as described in the Layer Info section of the documentation.
Hope this helps,