In presumtion that mb is talking about the 5.8 on 1/11/01.

Comparing the USGS NEIC list with the Canadian list it appears that there are additional differences where the NEIC has an Mb 4.9 on 1/13 that isn't on the Canadian list. Also the NEIC list is missing a whole lot of M3.0 - M3.6 quakes
that the Canadian list is listing during that time period. Also, for additional events on 1/23, the NEIC is listing larger magnitudes then the Canadian list for the quakes that are on both lists. And some of the locations are slightly a bit off from each other.

What does all this say? Nothing really. Some seismometers will pick up things that others won't. Sometimes seismometers will be off line for some reason or another and will miss picking up the event. That is part of the reason for
analysis taking a long time in getting the catalogs updated. Another reason is the number of phases where they have to have a certain number of them before they'll consider a quake a quake. Another problem is that in some locations, seismic waves will appear larger or be more scattered then in other areas because of where the seismometers are located. One located in soft soil will give entirely different readings then one located on rock.

All in all, there is really a lot that goes into this.

Below are the listings of quakes from both sites for the time period in question. I only kept the quakes on the Canadian list that matched up to the NEIC list for brevity.

NEIC: Earthquake Search Results

U. S. G E O L O G I C A L S U R V E Y

E A R T H Q U A K E D A T A B A S E

FILE CREATED: Thu Feb 1 16:48:05 2001
Circle Search Earthquakes= 7
Circle Center Point Latitude: 49.507N Longitude: 128.766W
Radius: 200.000 km
Catalog Used: PDE
Date Range: Year: 2001 - 2001 Month: 01/Day: 06 Month: 01/Day: 25
Magnitude Range: 2.5 - 6.5
Data Selection: Historical & Preliminary Data

CAT YEAR MO DA ORIG TIME LAT LONG DEP MAGNITUDE IEFM DTSVNWG DIST
NFPO km
TFS

PDE-Q 2001 01 11 000406.53 49.20 -128.87 10 6.10 MwGS ...G ....... 35
PDE-Q 2001 01 13 110237.81 49.27 -128.89 10 4.90 mb GS .... ....... 28
PDE-Q 2001 01 20 001426.71 50.71 -129.76 10 5.40 MwHRV ...G ....... 151
PDE-Q 2001 01 23 093923.39 49.44 -128.82 10 5.70 MwGS ...G ....... 7
PDE-Q 2001 01 23 144315.05 49.51 -128.77 10 5.50 MwHRV ...G ....... 0
PDE-Q 2001 01 23 145412.86 49.29 -128.99 10 4.40 mb GS .... ....... 28
PDE-Q 2001 01 23 151530.09 49.43 -128.31 10 4.00 mb GS .... ....... 34

from: http://www.seismo.nrcan.gc.ca/recent_canadian_eq/recent_canadian_eq_e.html
DATE TIME(UT) LAT LONG DEPTH MAG AGNCY REGION AND COMMENT
---- -------- --- ---- ----- --- ----- ------------------
2001/01/11 00:04:03 48.89N 129.31W 10.0G 5.8MS PGC WEST OF VANCOUVER ISLAND, B.C.
2001/01/20 00:14:23 50.49N 130.35W 10.0G 4.9ML PGC WEST OF VANCOUVER ISLAND, B.C.
2001/01/23 09:39:25 49.33N 128.79W 10.0G 4.6ML PGC WEST OF VANCOUVER ISLAND, B.C.
2001/01/23 14:43:12 49.17N 129.10W 10.0G 4.8ML PGC WEST OF VANCOUVER ISLAND, B.C.
2001/01/23 14:54:12 49.26N 128.96W 10.0G 3.9ML PGC WEST OF VANCOUVER ISLAND, B.C.
2001/01/23 14:54:12 49.26N 128.96W 10.0G 3.9ML PGC WEST OF VANCOUVER ISLAND, B.C.
2001/01/23 15:15:25 49.08N 129.25W 10.0G 3.6ML PGC WEST OF VANCOUVER ISLAND, B.C.

Dennis