Non-conventional oil is a recent phenomenom; and u are correct, mainly 'cuz of price barriers.  And surely the Resource Growth since 1997 reflects that (eg - OGJ adding Canadian tar sands back in 2002).

But look at Resource Growth previous to that and compare to Discoveries on the ASPO graph for the same period:

1960's - 278-Gb Resource Growth
1970's - 254-Gb   "
1980's - 325-Gb   "
1990's - 431-Gb   "

1288-Gb of Resource Growth in 40 years.  Incredible numbers!  In 1960, there was 660-Gb of Resoureces remaining.  Add 1288 in Discoveries and Reserve Growth and the total is 1948-Gb.  832-Gb has been consumed in that 40 year period.  That means we should have 1116-Gb left in Y2K.  I don't recollect the total of Discoveries from 1960 to Y2k, but when one deducts that figure from 1288-Gb, that gives us the Reserve Growth of conv oil.  Anyone?

Ok, Jean Laherrere's figures show approx just under 1000-Gb were discovered in that 40yr period.  That leaves a net of 300-Gb or 7.5-Gb/yr in Reserve Growth!  To give this some scale, the globe consumes 31-gb/yr & discoveries in the same 40 year period averaged 25-Gb/Yr.
I don't know were you got that figures from before 1995, because I take Jean laherrere's study he did with the french geologists perrodon and another fellow (don't recall the name) in 1994 for petroconsultants as a starting point. At this time they estimated a range between around 1600 to 2250 billion barrels for URR of conventional oil. Not long after independent estimates by Jean laherrere led him to believe in an URR of 2150, now this has been revised downwards to 2000 billion barrels. So please cite the reference to these figures,
We are not in disagreement, Rembrandt.  You seem to have forgotten to deduct the pre-1960 URR (723-Gb) from the 1750-Gb tally in that Laherrere/Perrodon/Demaison study.