Japan’s biggest union group reported the biggest wage gains in more than three decades for two successive years, but the broader picture for pay trends may not be quite as rosy, according to one think tank.

The Japanese Trade Union Confederation, known as Rengo, said 66% of the unions under its umbrella won pledges from employers for base pay increases in annual wage negotiations, or shuntō, this spring, with up to another 30% getting commitments for boosts to overall compensation. Meanwhile, a survey of 12,817 companies by Shinkin Central Bank Research Institute found that only 51% committed to base wage hikes, the think tank announced on Thursday.

The discrepancy between the two results stems from differences in coverage. A majority of the companies that come under Rengo’s purview have at least 100 employees, with internal unions organized to lobby on behalf of staff. Almost all of those surveyed by Shinkin have fewer than 100 workers, and most lack labor organizations.