Bollinger band width and %B on weekly charts

I may have found an interesting pattern on weekly charts using Bollinger bands width and %B (%B is a percentage that expresses the position of the price within the range described by the two bands, where 0% is the lower band and 100% is the higher band).

Multi-month drops in price coincident with a widening band, followed by a "topping" phase in the band width coincident with a rise in %B, indicate times when it may be advantageous to enter a long position.

I think it makes sense because that pattern describes an intermediate-term oversold position. 

The bands become wider when the price drops suddenly (they also widen when the price climbs, but that's another case). When an extreme oversold condition is reached, %B displays a spike low.  Afterwards, it starts climbing off the low, while the bands narrow again, as in a return to "normality". These are times when it's good to add long positions.  Of course, it has to be in the context of an underlying (1-2 years) uptrend.

I checked a few index funds and GLD and it seems to hold in most cases. I didn't verify it on any individual stock.