†This is where logic or mathematics operates differently from human language (aka natural language). Strictly speaking and mathematically speaking,
1. "N is Y, if not Z" would be read as
2. "if N is not Z, then N is Y".
However, in many human languages, English included, saying 1 doesn't mean just 2. To understand this, we should think a little about the motive of a speaker who said 1.
Quite likely, the speaker's intention was
3. "If N is not so great as Z (or any quantity > Y), it is = Y"‡.
But to say 3 exactly in those words would be clumsy,
and thus the speaker would naturally rephrase 3 as:
4. "N = Y if N ≠ Z",
or in plain English: 5. "N is Y, if not Z".
We can try another approach to show that if not can be used to mean perhaps even.
Let N is the number of people who has an attribute Q.
Consider these two following propositions:
(a) N is Y, if not Z.†
(b) N is Y, perhaps even Z.
Let Na is the set of all possible values of N for proposition (a).
It is easy to see that Na = {Y, Y+1, Y+2, Y+3, ..., Z}.
Let Nb is the set of all possible values of N for proposition (b).
It is also easy to see that Nb = {Y, Y+1, Y+2, Y+3, ..., Z}.
Now, it is clear that Na and Nb are equal. Hence, (a) and (b) are equivalent.
Thus, if not can be used to mean perhaps even.
Q.E.D.
It may make not much sense until you read it in the context of Scrum or Agile software development.
According to Wikipedia, spike is:
A time boxed period used to research a concept or create a simple prototype. Spikes can either be planned to take place in between sprints or, for larger teams, a spike might be accepted as one of many sprint delivery objectives. Spikes are often introduced before the delivery of large or complex product backlog items in order to secure budget, expand knowledge, or produce a proof of concept. The duration and objective(s) of a spike is agreed between product owner and development team before the start. Unlike sprint commitments, spikes may or may not deliver tangible, shippable, valuable functionality. For example, the objective of a spike might be to successfully reach a decision on a course of action. The spike is over when the time is up, not necessarily when the objective has been delivered.
The use of Spike on { how to / replacing } in the records you found is just the use of spike as a verb, which basically means "research a concept or create a prototype". Your guess is really close!
Best Answer
One definition of "Critical account" is "A response/analysis that analyses the validity of an author's claims.". In other words it is a comprehensive and carefully written book or article in which the author fully justifies each of his arguments and facts. All relevant questions are answered.