Bottom Line Up Front: The DFARS states the Small Business Specialist documents their review on the DD 2579 before the solicitation or contract modification is issued for acquisitions over $10,000. However, the FAR states the Agencies shall establish procedures including dollar thresholds for reviews, so you need to check AFFARS and your local agency policy as well. The $10,000 threshold in DFARS is not all inclusive. The PGI for instance states that any contract mod that increases the scope and any order under an FSS contract needs to be reviewed as well. References that I think are applicable to your question are found below:
FAR 19.202 Specific policies.
In order to further the policy in 19.201 (a), contracting officers shall comply with the specific policies listed in this section and shall consider recommendations of the agency Director of the Office of Small and Disadvantaged Business Utilization, or for the Department of Defense, the Director of the Office of Small Business Programs, or the Director’s designee, as to whether a particular acquisition should be awarded under subpart 19.5, 19.8, 19.13, 19.14, or 19.15. Agencies shall establish procedures including dollar thresholds for review of acquisitions by the Director or the Director's designee for the purpose of making these recommendations. The contracting officer shall document the contract file whenever the Director's recommendations are not accepted, in accordance with 19.506.
DFARS 219.201 General policy.
(c) For the defense agencies, the director of the Office of Small Business Programs must be appointed by, be responsible to, and report directly to the director or deputy director of the defense agency.
(8) The responsibility for assigning small business technical advisors is delegated to the head of the contracting activity.
(10) Contracting activity small business specialists perform this function by—
(A) Reviewing and making recommendations for all acquisitions (including orders placed against Federal Supply Schedule contracts) over $10,000, except those under the simplified acquisition threshold that are totally set aside for small business concerns in accordance with FAR 19.502-2. Follow the procedures at PGI 219.201 (c)(10) regarding such reviews.
(B) Making the review before issuance of the solicitation or contract modification and documenting it on DD Form 2579, Small Business Coordination Record (see PGI 253.219-70 for instructions on completing the form);
DFARS PGI 219.201 General policy.
(c)(10)(1) Agencies are not precluded from requiring that actions over $10,000, but under the simplified acquisition threshold, that are totally set aside for small business be reviewed by the small business specialist. One example of when an agency may choose to require this review is when the agency determines that such a review is necessary to assist contracting officers in identifying opportunities for other small business set-aside programs (e.g., HUBZone, service-disabled veteran-owned, small disadvantaged business, women-owned small business) in order to meet small business goals.
(2) Modifications that increase the scope of the contract, or the order under a Federal Supply Schedule contract, should be reviewed by the small business specialist. At a minimum, these actions might impact the small business subcontracting plan. However, funding modifications or modifications that do not increase the scope of the contract generally should not be reviewed, because the value that a small business specialist review would add in these instances would be minimal compared to the resources that would be expended.