Sadly, many projects are still using “traditional” methods (which seems to be one of the new names for waterfall). One of the drawbacks of this approach is that the time scales are relatively quite large compared to Scrum, which also means there are fewer time periods to measure. There is simply less data available is you have two six month buckets versus 12 one month buckets. This is one reason that “traditional” projects do not typically end up producing a team velocity. This in turns make it substantially challenging to estimate how long the next project will take.
There is however other data that can be mined so as to uncover this more fine grained time measurements we are looking for. The data in question lives in your requirement tracking system, bug database and source code control system. While these systems are often, shall we say imprecise, they do contain useful data.