There is, in fact, no indication anywhere in the original reference that these samples were from the "Pennyslvanian"; nor is there any hint that they were expected to be "300 million years old"; these appear to be purely apocryphal embellishments to the original account.
Surely, what the Russians intended to convey (and what nearly everybody would understand), is that these samples were charcoal from a not too ancient campfire.
This is evident first of all by the fact that it is part of a date list which is broken into three parts: "geologic samples", "archaeological samples", and "fossil animals".
Clearly, Pennsylvanian coal would be listed as a geologic sample, but this sample of "coal" is listed as an archaeological sample. In the original reference the sample is described as "scattered coals in a loamy rock in deposits of a 26-m [river] terrace".
Expansion of a deque is cheaper than the expansion of a because it does not involve copying of the existing elements to a new memory location.