Dave Kimble points out that while some models ran information based only on the data that they had in 1972, other models factored in a potential doubling of resources, especially as most resource discovery phases had not yet obviously peaked. See the graphs on his page.
As described in the exponential reserve index section, it is claimed that Limits to Growth predicted oil running out in 1992 among other natural resources. It should be noted, however, that the authors of the report accepted that the then-known resources of minerals and energy could, and would, grow in the future, and consumption growth rates could also decline. The theoretical expiry time for each resource would therefore need to be updated as new discoveries, techonologies and trends came to light. To overcome this uncertainty, they offered an upper value for the expiry time, calculated as if the known resources were multiplied by two. Even in that case, assuming continuation of the average rate of consumption growth, virtually all major minerals and energy resources would expire within 100 years of publication (i.e., by 2070). Even if reserves were two times larger than expected, ongoing growth in the consumption rate would still lead to the relatively rapid exhaustion of those reserves.