TCR Topical Index - Bold vs Not Bold verses

Bob

I've yet to understand the distinction between the bold references and regular font style.

The information at the beginning of the TI says:

"Bible references in BOLD indicate the Chain Verses of a topic".

This is confusing to me.  As an example, see pic, why is Jn 10,14 bolded once, and regular font 3 other times.  Sorry to be so dense here, but the light bulb hasn't turned on yet.

Bob

Bob

I found this information:

Those references cited in bold print represent the Chain Verses (prominent verses which may be traced from beginning to end within the text using the Forward Reference Number).

Frank Charles Thompson and John Stephen Jauchen, eds., Thompson Chain Marginal Notes (Updated and Expanded.; The Thompson Chain-Reference Bible; Indianapolis, IN: B.B. Kirkbride Bible Co., Inc., 1997), xiii.

That makes sense now, but now ask why are the regular font verses not considered to be part of the chain?  

Bob