Jurisdiction Boundaries Question

[Ma_playa]

What is the name of your state (only U.S. law)? MA

This question is a continuance of my previous questions. I got pulled over 1/3 of a mile into East Boston on Bennington Street from being in Revere on Bennington St.

My question is once I cross over into "Boston City Limits" shouldn't a speed limit sign be posted at that point where Revere ends on Boston begins?

I ask this because reading the MUTCD says:

Section 2B.18 Location of Speed Limit Signs

Standard:
Speed Limit (R2-1) signs, indicating speed limits for which posting is required by law, shall be located at the points of change from one speed limit to another.

At the end of the section to which a speed limit applies, a Speed Limit sign showing the next speed limit shall be installed. Additional Speed Limit signs shall be installed beyond major intersections and at other locations where it is necessary to remind road users of the speed limit that is applicable.

Speed Limit signs indicating the statutory speed limits shall be installed at entrances to the State and at jurisdictional boundaries of metropolitan areas.

If there is no speed limit sign on the Boston limit how am I too know what speed to follow since the last sign on the Revere side said 40MPH but had a 20MPH when flashing school sign about .6 of a mile from where i was pulled over at!

Any thoughts on this matter?