You probably know that FAQ stands for Frequently Asked Questions, but you don't know what PFAQ is, and that is because I just made it up. It stands for Potentially Frequently Asked Questions. This site is brand new and it would be a bit presumtious to claim there are frequently asked questions so I've made a list of what people are likely to ask. Hopefully, in time it will turn to be a real FAQ...
There is more good stuff for those who register (it's free of course), and it should be ready in a couple of weeks
The short answer: Yes, for the most part. There are some exceptions, which will be corrected in time.
The long answer: The calendaric dates in the database are exact. The problem is that there are two main calendars that have been used in the Western world. The first was the Julian calendar, which is the calendar used until the Gregorian calendar was introduced in October 15, 1582 (or October 5, 1582 in the Julian calendar). However, some countries did not accept the Gregorian calendar until much later. For example, Britain converted in 1752, The USSR in 1918 and Greece in 1923. The database will give exact results for dates before October 15, 1582 and for dates after 1923. It may also give the exact number of days that have passed for dates in the interval between 1582 and 1923, provided the country that published the date in question had already converted to the Gregorian calendar.