Old MBTA streetcar numbering (not the 4-digit internal system)

[SPUI]

http://206.103.49.193/boston/htm/bos019.htm shows a streetcar with a 152
number up top. http://www.sidis.net/Trans27.htm indicates that these
numbers were once used on the whole system, providing the following
(with post-1942 numbers):

152 Elevated (Blue Hill Avenue at Franklin Fark towards Dudley) - 22

410 Chelsea - Maverick via Meridian Street - 114

416 Chelsea - Maverick via Central Avenue - 116 or 117?

419 Gladstone Street - Maverick - 115

655 Woodlawn - Sullivan - 110

751 North Cambridge - Harvard - 82

When were these numbers used, and was there any relation to the internal
four-digit numbers?

[rtspcc]

Those were Hunter sign boxes. They were used from about 1911 to 1917.
Those were the internal route numbers at the time. Following the
recommendations of consultant John Bieler in 1918, the Boston El
reorganized much of their surface line network. They eliminated a lot
of duplicating lines. That's when they went from a three digit number
to a four digit number and the first attempt at using public route
numbers was eliminated.