Looking at the difference in party support in BC on election day

I thought it would be interesting to see how closely the difference in support between the two main parties correlates to the number seats the governments wins.

Election   Major party vote share        diff  govt seats
2001 - Liberal   57.62% NDP     21.56%  +36.06  97.47%
1949 - Coalition 61.35% CCF     35.10%  +26.25  81.25%
1945 - Coalition 55.83% CCF     37.62%  +18.21  77.08%
1956 - SoCred    45.84% CCF     28.32%  +17.52  75.00%
1963 - SoCred    40.83% NDP     27.80%  +13.03  63.46%
1969 - SoCred    46.79% NDP     33.92%  +12.87  69.09%
1966 - SoCred    45.59% NDP     33.62%  +11.97  60.00%
1933 - Liberal   41.74% CCF     31.53%  +10.21  72.34%
1975 - SoCred    49.25% NDP     39.16%  +10.09  63.64%
1937 - Liberal   37.34% Cons    28.60%  +8.74   64.58%
1972 - NDP       39.59% SoCred  31.15%  +8.44   69.09%
1991 - NDP       40.71% Liberal 33.25%  +7.46   68.00%
1986 - SoCred    49.32% NDP     42.60%  +6.72   68.12%
1960 - SoCred    38.83% CCF     32.73%  +6.10   75.00%
1983 - SoCred    49.76% NDP     44.94%  +4.82   61.40%
2005 - Liberal   45.80% NDP     41.52%  +4.28   58.23%
2009 - Liberal   46.02% NDP     42.06%  +3.96   57.65%
1979 - SoCred    48.32% NDP     45.99%  +2.24   54.39%
1941 - Liberal   32.94% CCF     33.36%  -0.42   43.75% 
1996 - NDP       39.45% Liberal 41.82%  -2.37   52.00%
I left out the 1952 and 1953 elections because a different voting system was used 
After the 1941 election the Liberals and Conservatives formed a coalition government
Highlighted dates are elections that saw a change in government

What patterns can I see here?   There is a board connection between how much the government won over the second place party by though there are exceptions to this such as in 1963 and 1966 Social Credit underperformed and in 1960 Social Credit  and 1996 NDP both overperformed.

What the pattern seems to indicate is that if the NDP manages to finish 15 percentage points ahead of the Liberals on election day, the NDP will likely take about 62 to 65 seats.  If they finish 7-8 percentage points ahead they are likely to take 58 to 60 seats.  If the NDP is 20 percentage points ahead, this would point to 68 to 69 seats.