fairviewhill: Some references to the necessity or not of filling all gaps: stockcharts, 'Gaps are a significant technical development in price action and chart analysis, and should not be ignored. Japanese candlestick analysis is filled with patterns that rely on gaps to fulfill their objectives.';
dummies.com, 'How do you know whether a gap will be filled? If it’s a breakaway gap, it probably won’t be filled — at least, not in the near future.'
livecharts.co.uk., 'Common myth: All gaps must be filled. This a very tempting intra-day strategy but is strictly speaking, not true.'
I thought they all had to be filled; however, I have found some published notes that dispute that.
Hope this helps. :)