Besides a multiplier, how can the Section B prices be considered "evaluated" from an analysis of the smaple task alone? Does the total contract value of the basic contract require "evaluation" since no money is issued until the task order level and cost/price evaluation will take place then?
How something will be evaluated will depend on what the requirements in the solicitation stated. In your question you used words or phrases like, "multiplier", "sample task", and "total contract value". Each of these means something different. Because I do not know what was actually stated in the solicitation, I will have to make some assumptions in order to provide you with an answer.
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First, FAR Sub-part 16.504(a)(4) (Indefinite-Quantity Contracts) clearly spells out certain requirements that a solicitation and contract for an indefinite quantity must have, such as period of performance to include options, total minimum and maximum quantities, SOW, single vs. multi award, etc. This subpart (16.504 (a) also states that quantity limits may be stated as a number of units or as dollar values.
Second, FAR Sub-part 15.402 (b)(Pricing Policy) states to price out each contract separately and independently.
Third, FAR Sub-part 15.404-1 (Proposal analysis techniques) provides several different methods for determining a fair and reasonable price to include price analysis, cost analysis, or cost realism analysis. Under FAR Sub-parts 15.404-1 (b) and (c) there are various techniques and procedures (such as parametric estimating methods, published price lists, IGE, etc.) for ensuring a fair and reasonable price.
Assuming your solicitation is in compliance with the aforementioned FAR Sub-parts and the fact that you stated that Section B of the solicitation CLIN pricing has not been established, then you could use the total proposed contract value to evaluate each offeror's proposed cost. In the question and question background, you mentioned a "sample task" and "sample task (order) pricing". I am not sure exactly what you mean by these terms. If you are stated that the solicitation included a sample task order that offerors were supposed to cost (price) out then this could possibly be used for evaluation purposes as long as you are in compliance with the above mentioned conditions/assumptions and it was stated in your solicitation that this is how proposals would be evaluated.
Since we do not have all of the facts particular to your contract, program, and situation, we highly recommend that you consult with your KO/CO and Legal Office for further guidance.